Patent GB-800036-A (GB)
Title: Improved writing instrument and liquid lead composition therefor
IPC: B43K7/01
Filed: 1955-05-11
Abstract: A writing liquid suitable for use in a ballpoint writing instrument (see Group XV) comprises a dispersion of carbon black in a viscous, resinous liquid vehicle.  The dispersion is such that it is partially flocculated under static conditions, can be broken down sufficiently by the shearing action of the ball point during writing, and will reflocculate on the writing surface so that the writing can be erased.  Examples of the liquid vehicle are polyester resins, mineral oil ester gum varnish and polymerized hydrocarbons.  Carbons specified are lamp black, furnace black, channel black or thermal black or graphite.  The proportions are approximately 2 to 14 parts of carbon black to 100 parts of the liquid vehicle by weight where the writing liquid is gravity fed to the writing ball; where the writing liquid is pressure fed to the ball, then there are 20-25 parts of carbon black to 100 parts of the liquid vehicle.  The size of the individual carbon black particles (unflocculated) ranges from 0.01 to 0.4 microns.  In one example of preparing the writing liquid, 1 part of an ester gum is dispersed in 4 parts of a mineral oil, then heated to 200-250 DEG  F. and filtered while hot.  Then 5 parts of this vehicle are mixed with 1 part of lamp black, heated to 170-180 DEG  F. for 18-24 hours, cooled, passed through a steel roll mill, then mixed with an additional quantity of the vehicle so that the resulting components are in the ratio 100 parts of the vehicle to 9 parts of the lamp black.  The whole is mixed and heated at 170-180 DEG  F. for 1-2 hours, cooled, passed through a mill, placed in a vacuum chamber and heated to 170-180 DEG  F. while under a vacuum of 2711 of mercury, for one hour.  The liquid is then filtered and bottled.  In Example (8) a dispersion of graphite in alcohol sold under the name "Dag" (Registered Trade Mark) is mixed with dipropylene glycol, triethanolamine tetrahydrofurfuryl alcohol and an "Amberol" resin.ALSO:In a liquid "lead" composition for use in a ball-point writing instrument comprising a mixture of carbon and a resinous liquid vehicle, the mixture is in such proportions that it is flocculated to such a degree as not to pass the ball-point when the instrument is not in use but, when subject to the shearing action of the ballpoint as it rotates during writing, is deflocculated sufficiently to pass round the ball-point on to a writing surface, whereon it reflocculates so that the carbon deposit remains on the surface of the paper and the mark made thereby can be erased by the usual type of rubber eraser. Specified proportions are 2-14 parts of carbon to 100 parts of vehicle by weight.  Specified types of carbon are lamp, furnace, channel or thermal blacks, or graphite, while the vehicles employed are bodied oils, resinous varnishes and polymerized hydrocarbons.  In examples: (1) the vehicle comprises one part of ester gum dissolved in four parts mineral oil and one part of lamp black is mixed with 5 parts vehicle.  The mixture after heating to 170-180 DEG  F. for 18-24 hours and cooling is passed through a three-roll steel mill and the viscous paste thus formed is mixed with an additional quantity of vehicle so that a product is obtained consisting of 100 parts vehicle to 9 parts lamp black. Examples 2-7 describe the production of liquid leads employing polyester resins, non-drying alkyd resins, and polymerized hydrocarbons as vehicle.  In Example 8 a graphite in alcohol dispersion sold under the name of "Dag" (Registered Trade Mark) is mixed with dipropylene glycol, triethanolamine, tetrahydrofurfuryl alcohol and "Amberol" resin.